Recently, there has been considerable interest within the detergent industry for laundry detergents which are "compact" and therefore, have low dosage volumes. To facilitate production of these so-called low dosage detergents, many attempts have been made to produce high bulk density detergents, for example with a density of 650 g/l or higher. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers.
Generally, there are two primary types of processes by which detergent granules or powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent granules. In the second type of process, various detergent components are mixed after which they are agglomerated with a nonionic or anionic detergent paste that also serves as the binder for the agglomerated particle itself. In both processes, the most important factors which govern the density of the resulting detergent granules are the density, porosity and surface area of the various starting materials and their respective chemical composition. These parameters, however, can only be varied within a limited range. Thus, a substantial bulk density increase can only be achieved by additional processing steps which lead to densification of the detergent granules.
The art is replete with processes directed primarily to densifying or otherwise processing spray dried granules. Currently, the relative amounts and types of materials subjected to spray drying processes in the production of detergent granules has been limited. For example, it has been difficult to attain high levels of surfactant in the resulting detergent composition, a feature which facilitates production of low dosage detergents. Thus, those skilled in the art have striven for ways in which detergent compositions can be produced without having the limitations imposed by conventional spray drying techniques. To that end, the art is also replete with disclosures of processes which entail agglomerating detergent compositions. For example, attempts have been made to agglomerate detergent builders by mixing zeolite and/or layered silicates in a mixer to form free flowing agglomerates. While such attempts suggest that their process can be used to produce detergent agglomerates, they do not provide a mechanism by which starting detergent materials in the form of highly active, viscoelastic surfactant pastes can be effectively agglomerated into crisp, free flowing, highly dense detergent agglomerates.
Additionally, a wide variety of problems have been encountered with handling high active, high viscoelastic surfactant pastes which are particularly useful in producing high density, high active detergent agglomerates suitable for modern low dosage detergent products. Such highly viscoelastic surfactant pastes are extremely sensitive to environmental and operating equipment parameters, all of which make the pastes difficult to transport, store and process when producing detergent agglomerates. By way of example, high active surfactant pastes typically must be kept at elevated temperatures to insure that they have a low enough viscosity to pump in and out of transport tracks or trains and in and out of storage tanks at the manufacturing facility. Any significant decreases in temperature may lead to undesirable gelling or solidification of the surfactant paste causing increases in manufacturing expenses and time. Note, however, that different rheological properties of the surfactant paste may result upon reheating.
This problem is especially exacerbated in the event that certain highly viscoelastic surfactant pastes exhibit non-linear viscoelastic properties, i.e. they exhibit elastic or "rubbery" flow properties during processing. The predictability of flow behavior of non-linear viscoelastic fluids is known to be very difficult. The unpredictability of flow behavior of such fluids lends itself to problems with handling and processing on a large-scale detergent manufacturing context. In the large-scale manufacturing context, a major problem with surfactant pastes that exhibit non-linear viscoelastic flow properties occurs when such pastes are pumped through equipment having complex geometries and/or converging and diverging sections, e.g. heat exchangers and manifolds converging into spray nozzles, during which pressure relief pins are blown causing undesirable shut-down time in the process.
Also in that regard, a high active viscoelastic paste requires an additional amount or buffer amount of carbonate and/or hydroxide so as to maintain the storage and transport stability of the surfactant paste before it is processed into a detergent product. However, the additional carbonate and/or hydroxide has the effect of increasing the viscoelasticity of the high active surfactant paste, therefore rendering it very difficult to process. The difficulty in processing arises due to a change in the viscoelasticity of the surfactant paste which requires relatively expensive high-pressure pumps, larger pipe lines and shorter transport distances to be implemented into the detergent-making process. As a consequence, it would be desirable to have a process in which the storage stability of the paste is maintained without sacrificing the its processability.
Accordingly, despite the above-mentioned disclosures in the art, there remains a need for a process by which high density detergent agglomerates can be effectively produced from a highly viscous and highly non-linear viscoelastic, aqueous surfactant paste. Also, there remains a need for such a process which is inexpensive and can be easily incorporated into large-scale production facilities for low dosage or compact detergents.